1. Field of Invention
The present invention is directed to polymer dispersed liquid crystal photovoltaic devices. It is envisioned that the invention may be used to convert solar energy to electrical energy.
2. Brief Description of the Prior Art
In spite of the widely appreciated magnitude of what has come to be called the energy crisis, there are still critical gaps in many methods currently available for energy generation. Specifically, despite recent advances in the field of renewable solar energy, current state of the art solar cells are inefficient, expensive and are limited in their application.
Recently, much attention has been directed towards the development of organic solar energy devices. Carbon nano-tubes (See Michael W. Rowell, et al., “Organic Solar Cells With Carbon Nanotube Network Electrodes,” Applied Physics Letters, vol. 88, pgs. 233506-1-233506-3 (2006); Ross Ulbricht, et al., “Transparent Carbon Nanotube Sheets as 3-D Charge Collectors in Organic Solar Cells,” Solar Energy Materials & Solar Cells, vol. 91, pgs. 416-419 (2007)), electrically conductive polymers (See G. Li, et al., “Efficient Inverted Polymer Solar Cells,” Applied Physics Letters, vol. 88, pgs. 253503-1-253503-3 (2006); Gavin A. Buxton, et al., “Computer Simulation of Polymer Solar Cells,” Modeling Simul. Mater. Sci. Eng., vol. 15, pgs. 13-26 (2007), published online on Dec. 12, 2006) and various types of liquid crystals (See Miguel Carrasco-Orozco, et al., “New Photovoltaic Concept: Liquid-Crystal Solar Cells Using a Nematic Gel Template,” Advanced Materials, vol. 18, pgs 1754-1758 (2006); Sandeep Kumar, “Discotic Liquid Crystals For Solar Cells,” Current Science, vol. 82, no. 0.3 pgs. 256-257 (2002)) have been investigated in an attempt to overcome the problems of the prior art. Although such organic solar energy devices have yielded higher quantum efficiencies, they have a lower overall power output than current silicon based solar cell designs.
The possible use of polymer dispersed liquid crystals (PDLCs) in solar energy devices has raised some interest because PDLCs are environmentally friendly, relatively inexpensive to manufacture and have relatively high energy conversion efficiency in comparison to conventional silicon solar cells. Nematic and chiral nematic liquid crystals, in particular, have been previously investigated. While these liquid crystals work well for optical applications, their relatively small molecular structures and lack of conjugated rings make them minimally photovoltaic and therefore not ideal for solar cell applications.
Additionally, PDLCs which have been incorporated in solar energy generation systems are structurally incapable of solar energy conversion. Rather these PDLCs are typically coupled to a conventional solar cell and function to focus light towards the solar cell. For example, U.S. Pat. No. 7,206,044 (hereinafter “Li”) discloses a solar cell in combination with a liquid crystal display. The liquid crystal display includes a cholesteric liquid crystal or polymer dispersed liquid crystal placed between opposing transparent plates (See col. 2, lines 11-17 of Li). A conventional solar cell is joined to one side of the liquid crystal display with a coupling layer such as a transparent adhesive material (See col. 2, lines 34-39 of Li).
U.S. Pat. No. 7,226,966 (hereinafter “Kambe”) discloses a composite material comprising polymers and inorganic particles for use in fabricating optical and electro-optical materials, optical devices and integrated optical circuits (See col. 4, lines 38-47 of Kambe). Kambe mentions the possibility of, but does not describe, a PDLC photovoltaic device. Rather, Kambe discloses that the composite material may include a polymer-dispersed liquid crystal display (See col. 30, lines 12-19 of Kambe) and self-assembling block copolymers (See col. 14, lines 17-23, 52-59 of Kambe) and that photonic crystals may possibly be used in the formation of solar cells (See col. 38, lines 27-33 of Kambe).
These patents, therefore, do not effectively disclose a PDLC material that functions as a solar cell. In general, the PDLCs used in prior art systems incorporate liquid crystals which filter light rather than absorb light and the polymer matrix is typically insulating rather than conducting.
Therefore, there exists a need to develop a PDLC that is capable of efficiently converting solar energy to electrical energy.